"I [I'll] have to wait until the market offers 50% off this November."
"I'll have to wait until the market gives its usual November discount of 50%."
"I'll have to wait for the 50% discount they offer every November."
The only problem with the original is that "the 50%" implies the hearer knows which 50% you're talking about.
I would use "I will have to wait", not "I have to wait."
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